Preparation of sulfuric esters of leuco vat dyes



Patented May 16, 1950 UNITED STATES ATENT OFFlCE PREPARATION OFSULFURIC'ESTERS OF LEUCO VAT DYE'S John Taras, Alpha, N. J., assignor toGeneral Aniline & Film Corporation, New York, N. Y., a corporation ofDelaware No Drawing. Application April 29, 1947, Serial No. 744,790

'7 Claims. (Cl. 260-321) 1 2 The present invention relates to theprepara- I have now discovered that contrary to the tion of sulfuricester salts of leuco vat dyes and accepted notion of prior operators,leuco vat dyes more particularly to the preparation of such ester can bereadily converted into their ester salts salts wherein theesterification is effected in an in a smooth operation leadin to highyields by aqueous medium. 5 operatin in an aqueous alkaline medium andIt is common practice at the present time to while utilizing as theesterifying agent the ademploy vat dyes in the form of their leuco esterdition products of sulfur trioxide with a pyrsalts rather than in theform of the simple leuco idine, such as, pyridine itself or a-picoline,procompounds. This is attributable to the fact that vided, however, thatcare is taken to insure a the leuco ester salts are much more solublethan proper correlation between the quantity of vat the leuco compoundsper se, a fact which fadye stuff treated with the quantity of the alkalicilitates the application of the reduced vat dyes utilized and thequantity of said addition prodto the fiber. uct. Unless such correlationbe maintained the Generally the leuco ester salts are preparedconclusion reached by prior operators that esby esterifying the leucocompounds by means of terification in an aqueous alkaline medium cantheaddition products of sulfur trioXlde and pyrnot be effected when usingthe addition product of idine in the presence of an excess of thepyrsulfur trioxide with pyridine as the esterifying idine. It is usual,too, to effect esterification agent proves to be true. simultaneouslywith the conversion of the vat It is undoubtedly correct that strongalkalies dyes to the leuco form and for this purpose there have atendency to split addition products of is normally employed a reactionmedium compyridine and sulfur trioxide in aqueous medium. prising thevate dye to be reduced and esteri- I have, for instance, repeated thework reportiied, a metallic powder such as iron powder, ed by Lecher atthe bottom of column 1, page 3, chlorsulfonic acid, cuprous chloride,and an exof his aforementioned patent and have found cess of pyridine.that the method in question fails to give ester- The reaction mixture inwhich such esterificaification probably because of the decompositiontion is effected is anhydrous. This is treaceable of the additionproduct. However, the delet0 the eneral impression of the art that theadterious action of the alkali on the addition proddition compounds ofsulfur trioxide with pyrnot of pyridine with sulfur trioxide mentionedidine hydrolyze spontaneously in aqueous media by Lecher does notmanifest itself with the proper and particularly in aqueous alkalinemedia. The proportioning of the components as I have obimpression alsopersisted that if the medium were served, It is ratherdifficult to statethe particstrongly alkaline in many cases the addition ularreasons whythis is so. The possibility exproduct decomposed by splitting of thepyridine ists that competing reactions tend to take place ring, as aconsequence of which no esterification in the esterifying mixtureinvolving the dyeu d p ss y ensue s fact is pha d in stuff, additioncompound and alkali and that in Lecher et a1. USP 2, 3,2 6, who prop s dto the quantities used by Lecher the reaction which p rate in an aqueousmedium but while employpredominates is splitting of the addition prodingas the esterifying agent e ad ion product, whereas, with the quantitiesof alkali which nets of sulfur trio ide wi h a u s r n r 40 I employesterification is the predominating retertiary amine than pyridine, e-,With tertiary action. However, irrespective of the theory or amineshaving a dissociation constant of at least reasons involved, t factremains t t b 1x1c at2-5C. erating as subsequently describedesterification The usual method of effecting reduction and or the vatdye proceeds smoothly with commerestelifioation o V dy s y Operatingcially satisfactory yields, a finding which is toin an anhydrous medium,is not o y eXpenSil/e tally unexpected in the light of the prior artfrom the standpoint of the materials used but teachings also from thedifiiculty involved in the conver- Itis, accordingly, an object of thepresent i sion of the dyestufis into the sulfuric ester salts ti n tproduce sulfuric ester alts of leuco in satisfactory yields. There has,therefore, been v t dyes while operating in an aqueous alkaline a verydecided need in the art to find a cheap medium and while utilizing theaddition prodprocess, particularly one which would permit the ucts ofsulfur trioxide and a pyridine as the esformation of the desired estersin high yields terifying agent.

while operating in an aqueous medium, that is, A-further object of thepresent invention is while avoiding the use of large amounts of costlythe esterification of the leuco vat dyes in an anhydroussolvent-diluents. aqueous alkaline medium while utilizing the additionproduct of sulfur trioxide with a pyridine as the esterifying agent andwhile correlating the amount of the leuco vat dye with the amount ofsuch addition product and the amount of the alkali employed.

Other and further important objects of the invention will becomeapparent as the description proceeds.

It will be apparent from What has been said that the crux of theinvention resides in the proper correlation of the quantities of thereactants. The alkali which is used both in the vatting and in theesterification steps must be a water soluble strong inorganic alkali,such as, sodium and potassium hydroxide and the like. Such compoundsmust be employed in the esterification mixture in a quantity rangingfromto about 40 mols for each mol of the leuco compound to be esterified.However, even if the alkali be employed in such quantities it isnevertheless imperative that a proper ratio be maintained between thequantity of vat dyestuff and of sulfur trioxide addition compound. It isabsolutely essential that there be used at least three mols of theaddition compound for each mol of the vat dyestuff if substantialesterification is to ensue. The quantity of the addition compoundgenerally ranges from 3 to 10 mols per mol of the vat dyestuff andpreferably increases Within this range as the quantity of the alkaliincreases. A greater quantity of the addition product than 10 mols permol of vat dyestuff may be employed, but since such greater quantityserves no useful purpose its employment is not recommended.

It must be pointed out that irrespective of the quantity of the additionproduct which is employed the desired esterification cannot take placeunless the proper quantity of alkali is used. Conversely, no matter whatthe quantity of the alkali, I have found that esterification is notpossible unless the quantity of the addition product amounts to at least3 mols per mol of vat dyestuff.

Any of the vat dyes may be esterified by my procedure, including theindigoid dyestuffs, the thioindigoid dyestuffs, the mixedindigo-thioindigo dyestuffs, indanthrenes, benzanthrones and the like.

However, the quinone vat dye intermediates, such as, the aminoanthraquinones, acetylamino anthraquinones and the like, are expresslyexcluded since my process is ineffective with such compounds. Thus, Ihave attempted to esterify leuco 2-acetylamino-3-chloroanthraquinonewhile utilizing quantities of the reactants within the aforestatedranges. The large excess of alkali, however, prevents the formation ofthe desired high yields of the di-ester and, in fact, appears to causethe formation of some other compound. The term vat dye as used hereinis, therefore, to be construed as covering quinonoid vat dyes but notintermediates for the manufacture of such dyes.

Examples of vat dyes which I have esterified by the method contemplatedherein are Jade Green or bz-2-bz-2-dimethoxy dibenzanthrone, 6.6-diethoxy-thioindigo, indigo, 5.5.7.7-tetrabromindigo, pentabromindigo,2-mon0bromindigo, 5.5-dichloro-6.6'-dibromindigo, 1.l'-dichlorindigo,6.6-diethoxy-thioindigo, the mixed indigos described in USP 1,925,217,the vat dyes disclosed in USP 1,809,224, the indanthrene vat dyesdisclosed in USP 943,717, 3.4.8.9-dibenzo-pyrene quinone, theindanthrene disclosed in USP 995,- 936, dibromated pyranthrone,dibrom-dimethoxydibenzanthrone, dichlor-isoviolanthrene and the like.

The addition product of the sulfur trioxide and pyridine orzx-IDlCOliIlQ, as the case may be, may be prepared by the usual methods.However, I have found that better results are at all times obtained ifsuch addition product be formed by slowly adding sulfur trioxide to acold solution of pyridine or picoline in a solvent, such as, chlorinatedhydrocarbons, i. e., chloroform, carbon tetrachloride,trichloroethylene, dichlorobenzene, and the like. Equally good resultsare obtained when using a mixture of a-picoline and pyridine, thepyridine being employed in excess to serve as an inert diluent.

The addition product of sulfur trioxide and pyridine can also beprepared by the action of chlorosulfonic acid on pyridine whileutilizing chloroform as the diluent. Under these circumstances, thesulfur trioxide addition compound separates as a white crystallineproduct, whereas, the pyridine hydrochloride remains dissolved in thechloroform.

My process is effected by first vatting the vat dye according to usualpractice, 1. e., by means of sodium hydrosulfite and an alkali andtreating the so obtained leuco compound with the sulfur trioxideaddition product. The latter step, which leads to the estcrification ofthe leuco compound, is generally effected at a temperature ranging fromabout room temperature, i. e., 20 C. to about 50 C. After theesterification is complete, the reaction mixture is generally treatedwith an oxidizing agent to oxidize any slight quantities of theunesterified leuco compound. For this purpose there may be employed thesodium salt of meta-nitro-benzene-sulfonic acid. After oxidation thesolution is heated in vacuo for the purpose of distilling off thepyridine. It is preferable during the entire operation to maintain thereactants in an inert atmosphere to thereby prevent premature oxidationof the leuco compound. This result may be achieved by operating in anatmosphere of nitrogen.

The following examples serve to illusrate the invention but it is to beunderstood that the invention is not restricted thereto. The parts areby weight unless otherwise stated.

Example I 15 parts of Jade Green are dissolved in a solution of 37.5parts of potassium hydroxide, 17.5 parts of sodium hydrosulfite, and 500parts of water.

The solution is then agitated while heating to a temperature of 70-75"C. under an atmosphere of nitrogen.

50 parts of the addition product of sulfur trioxide and pyridine arethen added to the blue vat at a temperature of 35 C. The reactionmixture is agitated at 35-40" C. for two hours while excluding air. Thedeep blue color of the leuco vat changes rapidly to a bluish red andafter about a half hour to a yellowish red. The formation of the lattercolor indicates that esterification of the leuco compound has beencompleted. This conclusion may be tested by extracting a small portionof the reaction mixture, bubbling air therethrough for a short time, andfinally filtering the test sample. If there be no further greenprecipitate on the filter paper, then the esterification may be deemedto be complete.

The solution is now diluted to two liters by the addition of water and 2parts of the sodium salt of meta-nitro-benzene sulfonic acid are addedfor the purpose of oxidizing any small quantities of the unesterifiedleuco com-pound. The solution is then heated to 45-50 C. and thepyridine removed by vacuum distillation. The solution is next filteredto remove the oxidized dyestuif which if present at all is filteredoffin very small quantites, never amounting to more than 5 parts of thetotal dyestuif charged and in most cases much less.

The resulting colored solution is stable to any further oxidativeaction. It dyes wool and cotton fibers a reddish brown .color which chans to the brilliant green color of the parent dyestuff when placed in asodium nitrate bath followed by immersion in dilute mineral acid.

If it be desired .to isolate .the potassium salt of the leuco.disulfuric acid ester, the red solution is concentrated under reducedpressure to a volume of efioccs. and there are added thereto a mixtureof 30 parts of potassium carbinate and 30 parts of potassium chloride.The potassium salt of the disulfuric acid ester precipitates incrystalline form. The yield is nearly quantitative, ranging from 90-95per cent. The product can be dispersed to a paste form which may be useddirectl for dyeing or printing by welllrnown methods.

The addition product of sulfur trioxide and pyridine is producedasfollows:

500 parts of pyridine and 1500 parts of chloroform are cooled to C.

523. parts of freshly distilled sulfur trioxide are added dropwise at10-20 CL, the end of the dropping funnel being placed beneath thesurface of the solution. The mixture is agitated for one hour at 25-30"6., filtered, and the presscake washed with200 parts of chloroform, andvacuum dried at a temperature below 50 C. There is thus obtained a whiteproduct melting at 120-121 C. and having a sulfur content of 20.14 percent. The yield is quantitative.

The addition product of sulfur trioxide and pyridine can also beproduced as follows:

A solution of'632 parts of pyridine and 2000 parts of chloroform arecooled to 0 6., and 385 parts of chlorosulfonic acid are added dropwiseto the solution while maintaining a temperature below 10 C. The mixtureis agitated for onehalf hour at 10 to20 C., filtered and the presscakewashed with .400 parts of chloroform. The white crystalline productobtained is dried below 50 C. in a vacuum. The dry product which isobtained in excellent yields is the addition product of sulfur trioxideand pyridine. It has a sulfur content of 20.12% and melts at 120 to 121C. The pyridine hydrochloride formed simultaneously in the reactionremains in the chloroform filtrate.

The critical nature of the quantity of reactants in the esterificationmixtureis very aptly demonstrated by the following comparison:

(a) The above procedure was repeated excepting that there was used 15.5parts of Jade Green and 7.7 parts of sodium hydroxide. No esterificationtook place.

(b) The procedure of Example I was again repeated while using 15.5 partsof Jade Green and 10.8 parts of potassium hydroxide. Here again noesterification was effected.

(c) The procedure of Example I was again repeated while utilizing 15.5parts of Jade Green, 37.5 parts of potassium hydroxide and 11.5 parts ofthe addition product of pyridine and sulfur trioxide. The conditionsobserved again fail to effect esterifica-tion.

6 '(d) The proce ure in Examp I- a repeate while utilizing 15.5 parts.of Jade Green, 200 parts of water. 7.7 par f sodium h d QX d 1-1 partsof sodium hydrosulfite and 11.5 parts of parts parts parts 91d Jadeparts alkali hydropyridine- (Raster Green sulfite S03 Per cm 15.0 37.5KOH (lngh)- 17.5 50 (high) 07.8 (a) 15. 5 7.7 N aOH flow) 17. 5 50(high) none (b) 15. 5 10.8 KOH (low) 17.5 50 (high) none (c) 15. 5 37:5KOH (high) 17.5 11.5 (10W) none (d) 15.5 7.7 NaOH (low)..- 7. G 11.5(low). Bone Example II 125 parts of Jade Green are added .to a solutionof 5000 parts of water 1:75 parts of powdered sodium hydrosulfite, and300 parts of potassium hydroxide.

To the vat thus obtained there are added 420 parts of the sulfurtrioxide addition product of a-picoline while maintaining an inertmosphere in the reactor. The mixture is agitated for several hours at35-40" C. The solution thus obtained is diluted with 15,000 parts ofwater, following which there are added 50 parts of the sodium salt ofmeta-nitrobenzene sulfonic acid and the mixture heated to 60 C. andfiltered.

The clear red filtrate contains the disulfuric ester of leuco JadeGreemwhich may be isolated as such if desired by concentrating thesolution under reduced pressure and salting out the dyestuff by means ofpotassium chloride and potassium carbonate as in Example I. Thecrystalline product which precipitates is separated by filtration andmay be made into a paste for printing andpadding. The yield ispractically quantitative, ranging from -95 per cent. The tinctorialproperties of the dyestuifcompare favorably with those ofestablishedcommercial brands of this product.

The addition product of sulfur trioxide and ,a-picoline may .be obtainedas follows:

1186 parts of a-picoline and 3000 parts of chloroform vare cooled to 10C. and

1000 parts of sulfur trioxide are then added while maintaining atemperature of 10-20 C. The sulfur trioxide-a-picoline addition productis isolated as described in Example I in connection with the sulfurtrioxide-pyridine addition product.

Erample III A vat is prepared .by treating .5 parts of Jade Green with asolution of 250 parts of water,

19 parts of potassium hydroxide, and

9 parts of sodium hydrosulfite.

To the clear blue vat so obtained there are added =at*25 -C'.,

30 parts of the sulfur trioxide-pyridine addition compound described inExample I. The reaction temperature is held at 25-30 C. for two hourswhile the reaction mixture is agitated under exclusion of air. Thedi-potassium salt of the disulfuric acid ester of leuco dimethoxydibenzanthrone is thus obtained and may be isolated as described inExample I.

Example IV 15 parts of 6.6-diethoxy thioindigo are vatted in a solutionof 500 parts of water, 40 parts of potassium hydroxide, and 18 parts ofsodium hydrosulfite.

When reduction of the vat dye is complete, there are then added to thesolution 65 parts of the pyridine-sulfur trioxide complex at atemperature of 10 C. The temperature is then allowed to rise to 25-30 C.and maintained at this level for several hours. At this time,esterification is complete and any unesterified leuco compound isdestroyed by oxidation with sodium-meta-nitro benzene sulfonate. Thepyridine is now removed by vacuum distillation, after which the solutionis filtered to yield an amber colored filtrate.

The disulfuric acid ester salt of the leuco diethoxy thioindigo may beisolated from the amber colored filtrate by salting out with a mixtureof potassium chloride and potassium carbonate. The di-ester of thedyestufi may be dried by known methods after which it is ready for usein the printing and padding of vegetable fibers by acid-oxidativedevelopment methods. The dyestufi yields bright orange printscharacteristic of diethoxy thioindigo.

Ezcample V 25 parts of indigo are vatted in a solution of 9'75 parts ofwater 35 parts of sodium hydrosulfite and '75 parts of sodium hydroxidewhile maintaining an atmosphere of nitrogen. To the vat thus obtainedthere are added 100 parts of the addition product of pyridine and sulfurtrioxide and the solution is agitated at 35-40 C. for several hours. Atthis point esterifioation is complete and the solution is diluted with1000 parts of water.

Example VI 25 parts of indigo are vatted as described in Example V andto the vat are added at a temperature of 35-40 C. 105 parts of theaddition compound of a-picoline and sulfur trioxide while excluding air.After oxidizing any of the unesterified leuco compound as in the aboveexamples, vacuum distilling the a-plCOliIlG, the solution is 8 filteredto yield a clear amber solution containing the disulfuric acid ester ofleuco indigo.

Example VII 25 parts of 5.5'.7.7-tetrabromindigo are vatted in asolution of 1000 parts of water 35 parts of sodium hydrosulfite andparts of sodium hydroxide.

To the vat thus obtained there are added parts of the addition productof pyridine and sulfur trioxide and the solution is agitated for severalhours at 35-40 C. while excluding air. The solution is next diluted with1000 parts of water and thereto are added 5 parts of sodiummetanitro-benzene sulfonate. After removing the pyridine by vacuumdistillation at 60 C., the solution is filtered to yield an ambercolored solution containing the disulfuric acid ester of leuco tetrabromindigo. The sodium salt of the ester may be isolated by concentratingthe solution under reduced pressure and salting out by the gradualaddition of soda ash and sodium sulfate.

The procedure was repeated while utilizing 34.6 parts of the tetrabromindigo, 17.3 parts of sodium hydroxide, 15.3 parts of sodium hydrosulteand 23 parts of the pyridine-sulfur trioxide addition product. In thiscase no esterification took place.

Example VIII A vat is prepared as described in Example VII from 25 partsof 5.5.'l.7'-tetrabrom indigo. When reduction is complete, i. e., whenthe blue color of the dyestufi disappears completely, 100 parts of thesulfur trioxide addition product of a-picoline are added and thesolution agitated for several hours at 35-40 C. in an atmosphere ofnitrogen. After oxidation of any of the unesterified leuco compound anddistillation of the a-picoline, the amber colored solution is filtered.The disulfuric acid ester of leuco tetrabrom indigo may be obtainedtherefrom in the form of its sodium salt by concentrating the solutionunder reduced pressure and salting out with sodium sulfate.

Emample IX The procedure is the same as in Example I excepting thatthere are used 30 parts of Jade Green '75 parts of potassium hydroxide35 parts of sodium hydrosulfite and 100 parts of the addition product ofsulfur trioxide and pyridine. The yield is 97.8 per cent of theory.

Example X The procedure is the same as in Example I excepting that thereare used 15 parts of Jade Green 30 parts of potassium hydroxide 13.3parts of sodium hydrosulfite and 45 parts of the addition product ofpyridine and sulfur trioxide. The yield is 95.3 per cent of theory.

Example XI The procedure is the same as in Example I excepting thatthere are used 15 parts of Jade Green 26.6 parts of potassium hydroxide11.6 parts of sodium hydrosulfite and 43.3 parts of the addition productof pyridine and sulfur trioxide. The yield is 99.7 per cent of theory.

Example XII The procedure is the same as in Example I excepting thatthere are used 15 parts of Jade Green 23.3 parts of potassium hydroxideparts of sodium hydrosulfite, and

40 parts of the addition product of sulfur trioxide and pyridine. Theyield is 85.3 per cent of theory.

Example XIII The procedure is the same as in Example VII, excepting thatthere are used 30 parts of the tetrabrom indigo 60 parts of potassiumhydroxide 30 parts of sodium hydrosulfite 90 parts of the additionproduct of pyridine and sulfur trioxide. The yield was 97.2 per cent oftheory.

Example XIV The procedure was the same as in Example VII excepting thatthere were used parts of the tetrabrom indigo 30 parts of potassiumhydroxide 15 parts of sodium hydrosulfite and The procedure is the sameas in Example VII excepting that threre are used 15.7 parts of thetetrabrom indigo 35 parts of potassium hydroxide 17 parts of sodiumhydrosulfite and 50 parts of the addition product of pyridine and sulfurtrioxide. The yield was 83.7 per cent of theory.

Example XVI The procedure is the same as in Example V excepting thatthere were used 62.8 parts of indigo 140 parts of potassium hydroxide 68parts of sodium hydrosulflte 200 parts of the addition product of sulfurtrioxide and pyridine. The yield was 81.8 per cent of theory 10 EwampleXVII The procedure is the same as in Example V excepting that there wereused 62.8 parts of indigo parts of sodium hydroxide 68 parts of sodiumhydrosulfite, and

200 parts of the addition product of sulfur trioxide and pyridine. Theyield of di-ester was 97% of theory. Various modifications of theinvention will occur to persons skilled in the art and I, accordingly,do not intend to be limited in the patent granted except as necessitatedby the prior art and the appended claims.

I claim:

1. A process for the production of watersoluble sulfuric ester salts ofleuco vat dyes by reacting a leuco vat dye with the sulfur trioxideaddition compound of a tertiary amine selected from the class consistingof pyridine and apicoline which consists in adding said additioncompound in the form of a preformed solid to a solution consisting of anaqueous alkaline solution of said leuco compound in which the alkali isa strong inorganic alkali while employing for each molecule of the leucovat dye from 10 to about 40 mols of alkali and at least 3 mols of saidsulfur trioxide addition compound and agitating the solution at atemperature ranging from about 20 to about 50 C.

2. The process as defined in claim 1 wherein the sulfur trioxideaddition product is the sulfur trioxide addition product of pyridine.

3. The process as defined in claim 1 wherein the leuco vat dye is aleuco indigoid.

4. The process as defined in claim 1 wherein the leuco vat dye is thatfrom Jade Green.

5. The process as defined in claim 1 wherein the leuco vat dy is thatfrom tetrabrom indigo.

6. The process as defined in claim 1 wherein the sulfur trioxideaddition product is the sulfur trioxide addition product of a-DiCOlillG.

'7. The process as defined in claim 1 wherein the quantity of additionproduct employed is greater the greater the quantity of alkali.

JOHN TARAS.

REFERENCES CITED FOREIGN PATENTS Country Date Great Britain Jan. 2.1,1926 Number Certificate of Correction Patent No. 2,507,944 May 16, 1950JOHN TARAS It is hereby certified that errors appear in the printedspecification of the above numbered patent requiring correction asfollows:

Column 5, line 13, for the Word nitrate read nitrite; line 19, forcarbinate read carbonate; column 10, lines 21 and 22, for a-picolineread a-pz'colt'ne;

and that the said Letters Patent should be read with these correctionstherein that the same may conform to the record of the case in thePatent Oflice.

Signed and sealed this 1st day of August, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

1. A PROCESS FOR THE PRODUCTION OF WATERSOLUBLE SULFURIC ESTER SALTS OFLEUCO VAT DYES BY REACTING A LEUCO VAT DYE WITH THE SULFUR TRIOXIDEADDITION COMPOUND OF A TERTIARY AMINE SELECTED FROM THE CLASS CONSISTINGOF PYRIDINE AND APICOLINE WHICH CONSISTS IN ADDING SAID ADDITIONCOMPOUND IN THE FORM OF A PREFORMED SOLID TO A SOLUTION CONSISTING OF ANAQUEOUS ALKALINE SOLUTION OF SAID LEUCO COMPOUND IN WHICH THE ALKALI ISA STRONG INORGANIC ALKALI WHILE EMPLOYING FOR EACH MOLECULE OF THE LEUCOVAT DYE FROM 10 TO ABOUT 40 MOLS OF ALKALI AND AT LEAST 3 MOLS OF SAIDSULFUR TRIOXIDE ADDITION COMPOUND AND AGITATING THE SOLUTION AT ATEMPERATURE RANGING FROM ABOUT 20 TO ABOUT 50*C.